For fruits and vegetables - Why is a bag needed at all ?

I just put my fruits and vegetables directly on the conveyor belt.

For most you don't. But if you buy loose cherry tomatoes, having 30 of them rolling around everywhere isn't exactly practical.

Thats easily solved though by simple buying some reusable fruit/veggie net. Essentially the same as what you would use for socks or underwear in the laundry.